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Extracellular Matrix Flashcards

1
Q

What is the extracellular matrix

A

Complex network of macromolecules (proteins and carbohydrates) deposited by cells which is made up of both fibrillar and non-fibrillar components. After being deposited, it becomes immobilised outside the cells and fills the spaces between the cells

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2
Q

what is fibrillar

A

fibre -making

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3
Q

what is ECM essential for

A

development, tissue function and organogenesis

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4
Q

key functions of ECM

A
  • provide physical support
  • determine mechanical and physiochemical properties of the tissue
  • influence of the growth, adhesion and differentiation status of the cells
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5
Q

what makes up the extracellular matrix in connective tissues

A

Collagens , Multi-adhesive glycoproteins and proteoglycans

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6
Q

examples of collagens in connective tissue

A

Type 1, 2,3 (fibrillar) and Type 4 (basement membrane)

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7
Q

examples of multi adhesive glycoproteins present in connective tissue

A

Laminins(basement membrane), fibronectin and fibrinogen

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8
Q

examples of connective tissues

A

tendon, bone, cartilage and vitreous humour (jelly that fills eye)

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9
Q

vitreous humour

A

soft and transparent

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10
Q

tendon and skin

A

tough and flexible

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11
Q

bone

A

hard and dense

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12
Q

cartilage

A

resilient and shock-absorbing

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13
Q

fibrotic disorders occur due to excessive ECM deposition

A

Liver fibrosis- cirrhosis

Kidney fibrosis or lung fibrosis

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14
Q

disorders due to excessive loss of ECM

A

osteoarthritis

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15
Q

describe the structure of collagen

A

made up of 3 alpha chains forming a left handed helix

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16
Q

Structure of Type 1 collagen

A

made of 2 genes so heterotrimer [α1(I)]2 [α2(I)]

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17
Q

Structure of Types 2 and 3 collagen

A

homotrimers, having only one chain type. Their compositions are therefore, [α1(II)]3 and [α1(III)]3

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18
Q

Primary sequence of collagen

A

The primary sequence of collagen proteins contains a characteristic glycine-x-y repeat where x is often proline and y is often hydroxyproline.

To form a stiff triple helical structure, every third position in the must be occupied by the amino acid glycine, as this is the only amino acid small enough to occupy the interior. R region of glycine is H

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19
Q

Hydrogen bond formation between collagen molecules

A

Hydroxylation of proline contributes to the H bond formation. These provide tensile strength and stability.
Both lysine and hydroxy-lysine residues are involved.

Crosslinking only takes place only after the collagen has been secreted.

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20
Q

how does vitamin C deficiency affect collagen

A

results in underhydroxylated collagens, with dramatic consequences for tissue stability (scurvy). This is due to the enzymes prolyl hydroxylase and lysyl hydroxylase requiring vitamin C as a co-factor for functionality.

21
Q

Collagen biosynthesis

A

Pro alpha chains in ER. Then a series of covalent modifications and folds occur folding the molecule into a triple-helical procollaged. Cleavage of propetide. Collagen. Fibril formation(if appropriate). Cross linking.

22
Q

Ehlers-Danlos syndrome

A

a group of inherited connective tissue disorders whose symptoms include stretchy skin and loose joints.

Several of these can arise due to mutations in collagen, which negatively affect collagen production, collagen structure or collagen processing.

23
Q

Examples of fibril forming collagens

A

9 and 12

24
Q

example of non-fibrillar collagen

A

collagen type IV, which is present in all basement membranes.

In the collagen IV network, the collagen type IV molecules can associate laterally between triple-helical segments as well as head-to head and tail-to tail between the globular domains to give dimers, tetramers and higher order complexes.

25
Q

What are basement membranes/basal laminae

A

Basement membranes are flexible, thin mats of ECM surrounding muscle, peripheral nerve and fat cells and most epithelia. Contain collagens, glycoproteins and proteoglycans. eg. basement membrane in kidney

26
Q

diabetic nehropathy

A

I​n the disorder diabetic nephropathy, there is an accumulation of extracellular matrix leading to a highly thickened basement membrane. This restricts renal filtration and can lead to renal failure.

27
Q

alport syndrome

A

I​n Alport syndrome, mutations in collagen IV result in an abnormally split and laminated GBM which is associated with a progressive loss of kidney function and also hearing loss.

28
Q

how is the extent of stretching of tissues controlled

A

by weaving collagen and elastic fibres together

29
Q

what are elastic fibred made of

A

a core of elastin and microfibrils which are rich in fibrillin

30
Q

structure of elastin

A

2 types of segments that alternate along the polypeptide chain: hydrophobic regions, and alpha-helical regions rich in alanine and lysine.

Many lysine side chains are covalently cross-linked. 

31
Q

what is marfans disease

A

due to disorders in protein fibrillin-2 and has some diverse manifestations involving skeletal, ocular and cardiovascular systems, individuals can be predisposed to aortic ruptures.

32
Q

2 multi-adhesive glycoproteins

A

Laminins which are associated with basement membrane and fibronectin

33
Q

Laminin structure

A

very large. they are heterortrimeric proteins made up of an α chain, a β chain and a γ chain, which form a cross shaped molecules

34
Q

muscular dystrophy/epidermolysis bullosa

A

Inherited diseases. caused froman absence of the α2 chain in laminin 2. Symptoms include hypotonia (abnormally decreased muscle tension), a generalised weakness and deformities of the joints.

35
Q

fibronectin

A

found in ECM but also body fluids. can exist as either insoluble fibrillar matric or soluble plasma protein. derived from a single gene, with alternate splicing of mRNAs giving rise to diff types. large molecule and is linked together by disulphide bonds

36
Q

role of fibronectin

A

regulate cell adhesion and migration , notably embryogenesis and tissue repair, wound healing (help to promote blood clotting).

37
Q

proteoglycans

A

core proteins which are covalently attached to one or more glycosaminoglycan chains (GAG chains)

38
Q

5 types of proteoglycans

A

Basement membrane proteoglycans
Aggregating proteoglycans
Small leucine rich proteoglycans
Cell surface proteoglycans

39
Q

Basement membrane proteoglycan

A

Perlecan

40
Q

Aggregating proteoglycan ( which interact with hyaluronan)

A

Aggrecan

41
Q

Small leucine-rich proteoglycan

A

Decorin

42
Q

Cell surface proteoglycan

A

Syndecans 1-4

43
Q

What are GAG chains

A

Repeating disaccharide units where one of two sugars is amino sugar ( a sugar where the hydroxyl group has been replaced by amine). GAGs can be surface or carboxylate and so carry a high negative charge which attracts Na + ions and water into ECM

44
Q

Cartilage and GAGS

A

Cartilage has a matrix rich in collagen with large quantities of GAGs trapped in the mesh work. Balance of swelling pressure is negated by the tension in collagen fibres which generates tensile strength

45
Q

4 main groups of GAG chains ( based on repeating disaccharide unit)

A

Hyaluronan, chondroiyin sulfate and Dermatan sulfate, heparin sulfate and keratan sulfate

46
Q

Hyaluronan

A

Found in soft connective tissues. Distinct from other GAGs as it is simply a carbohydrate without a core protein . Unsulfated and made up of repeating dissacharidases which can number up to 25,000.

All other GAGs are synthesised and attached to their core protein in the ER and Golgi apparatus inside cells

Highly polymerised and has a high volume

47
Q

Where can hyularonan be found

A

Vitreous humour of eye and in sink is, fluid of joints ( here it protects the cartilaginous surface from damage).

48
Q

Aggrecan

A

GAGs are highly sulfate which increases negative charge. There are also many negatively charge carboxyl groups and these attract cations like sodium which is osmotically active so a lot of water is drawn in. Water is given up under compressive load- so aggrecan is perfect for cartilage where you need to resist compressive forces

49
Q

Osteoarthritis

A

Erosive disease involved in excessive ECM degredation .cushioning of cartilage over ends of bone are lost. With increasing age, aggrecan is cleaved by aggrecanases and metalliproteinases and results in loss of aggrecan fragments to the synovial fluid

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